Add "We've Moved" notices to the Classic (non-Streams) SDP area,
now that SDP 2026.1 GA has shipped from the new //p4-sdp/main
Streams home.
This Classic area (//guest/perforce_software/sdp/...) is now
frozen as of SDP 2025.2 Patch 1, the last release shipped from
here. This change:
* Adds WeHaveMoved.md explaining the move, the new home, and the
new fixed download URLs.
* Adds a "this location has moved" banner to README.md and to each
of the generated doc HTML pages.
* Adds a one-line warnmsg to install_sdp.sh and upgrade.sh pointing
users to the new location, while leaving their actual
install/upgrade behavior for SDP 2025.2 Patch 1 unchanged.
* Removes the redundant doc/README.html (superseded by
WeHaveMoved.md / the updated README.md).
Nothing here is deleted or broken -- this area continues to work
exactly as before for anyone still using it, per SDP's normal N-2
support model (supported until SDP 2028.2 ships).